Battery pack and battery remaining power calculating method

ABSTRACT

The present invention relates to a battery pack having a function for calculating a remaining capacity of a battery cell that can be charged. When a calculated capacity integrated value Y is smaller than a maximum capacity integrated value Ym, a microcomputer ( 5 ) incorporated in the battery pack determines the capacity integrated value Y as the remaining capacity data of a battery. When the calculated capacity integrated value Y is the maximum capacity integrated value Ym or larger, the microcomputer determines the maximum capacity integrated value Ym as the remaining capacity data of the battery. Further, the microcomputer ( 5 ) corrects a reference capacity integrated value Y 0  on the basis of the number of times that the capacity integrated value Y reaches the maximum capacity integrated value Ym.

TECHNICAL FIELD

The present invention relates to a battery pack used as a power sourceof an electronic device such as a video camera, a portable telephone ora personal computer and a method for calculating the remaining capacityof a battery in the battery pack.

This application claims a priority based on Japanese Patent ApplicationNo. 2002-171828 filed in Jun. 12, 2002 in Japan and Japanese PatentApplication No. 2002-242650 filed in Aug. 22, 2002 in Japan. Theseapplications are applied to this application by referring to them.

BACKGROUND ART

A battery pack having a battery cell as a secondary battery capable ofcharging such as a lithium-ion battery, an NiCd battery, a nickelhydrogen battery, etc. has been hitherto employed. Such a kind ofbattery pack is used as a power source of an electronic device such as avideo camera, a portable telephone, or a personal computer or the like.

In the battery pack used as the power source of the electronic device,for instance, a microcomputer that calculates the remaining capacity ofthe battery and communicates with the electronic device using thebattery pack as the power source, a peripheral circuit of themicrocomputer, a state detecting circuit of the battery cell necessaryfor calculating the remaining capacity of the battery by themicrocomputer, and a nonvolatile memory in which data necessary forcalculating the remaining capacity of the battery is stored areincorporated.

The electronic device using the battery pack displays the remainingcapacity of the battery calculated by the microcomputer, for instance,in terms of time.

The remaining capacity of the above-described battery pack can berepresented by a capacity integrated value Y obtained by integratingelectric current flowing upon charging and discharging.

As disclosed in, for instance, Japanese Patent Application Laid-Open No.hei 9-285026, the capacity integrated value Y is obtained in such a waythat the capacity integrated value is reset to a reference value (referit to as a reference capacity integrated value, hereinafter) Y0 everytime the battery pack is charged and discharged and a current value isintegrated by regarding the reference capacity integrated value Y0 as areference.

As the reference capacity integrated value Y0, a capacity integratedvalue when the battery pack is charged to 90% as much as a full-charge,for instance, upon shipment is employed. In such a kind of battery pack,as a method for resetting the capacity integrated value Y to thereference capacity integrated value Y0, a method as described below isexemplified. That is, a current value Ix when the battery pack issubjected to a constant voltage charging operation before shipping toobtain the capacity integrated value Y=the reference capacity integratedvalue Y0 is stored in a nonvolatile memory together with the referencecapacity integrated value Y0, and then, when the battery pack undergoesthe constant voltage charging operation upon its use to obtain thecurrent value of Ix, the capacity integrated value Y is reset to thereference capacity integrated value Y0.

It has been known that the above-described battery pack has its capacityreduced with the lapse of time, that is, the battery pack isdeteriorated. When the battery pack is deteriorated, the differencebetween the remaining capacity of the battery calculated by themicrocomputer and an actual remaining capacity of the battery in thebattery pack is generated.

Accordingly, when the battery pack is deteriorated, the capacityintegrated value Y calculated by the microcomputer needs to becorrected.

As a method for correcting the capacity integrated value Y, a method isconsidered that, for instance, a prescribed coefficient is multiplied bythe capacity integrated value Y to correct the capacity integrated valueon the basis of causes that deteriorate the battery pack.

As the causes that deteriorate the battery pack, number of times ofcharging and discharging the battery pack, the use of the battery packand storage conditions, etc. may be exemplified.

In the battery pack, it has been known that as the number of times ofcharging and discharging the battery pack is more increased, thedeterioration of the battery pack is more advanced. For example, in thelithium-ion battery, it has been known that charging and dischargingoperations are performed 500 times to have a capacity as much as 60%.

The number of times of charging and discharging the battery pack can beobtained by a method disclosed in, for instance, Japanese PatentApplication Laid-Open No. hei 9-243718 or the like. Accordingly, thecapacity integrated value Y can be corrected on the basis of the numberof times of charging and discharging the battery pack.

As is known, a way of deterioration of the battery pack is changeddepending on using conditions or the storage conditions. Further, as isknown, for instance, when the battery pack is continuously used for along time or when the battery pack is used at low temperature or thelike, the battery pack is liable to be deteriorated. Japanese patentApplication Laid-Open No. 2000-260488 discloses a method for calculatingthe remaining capacity of a battery in accordance with temperaturechange.

However, all of the using conditions or the storage conditions of thebattery pack is hardly grasped. Accordingly, it is difficult to correctthe capacity integrated value Y in accordance with the using conditionsor the storage conditions of the battery pack.

As another method for correcting the capacity integrated value Y, amethod is considered that the degree of deterioration of a deterioratedbattery pack is actually measured and the capacity integrated value iscorrected on the basis of the recognized degree of deterioration.

The degree of deterioration of the battery pack is measured by what iscalled a five-hour method. The five-hour method is a method that afterthe battery pack is charged to a fully charged state from an emptystate, the battery pack is discharged for about 5 hours to measure thedegree of deterioration of the battery pack.

A charging time is different depending on capacities of batteries. Forinstance, in a battery pack “NP-FC10” (trade name) used in a digitalcamera produced by Sony Corporation, it takes about 3 hours to chargethe battery pack.

As described above, when the degree of deterioration of the battery packis actually measured, it takes about 8 hours. That is, when the degreeof deterioration of the battery pack is actually measured and thecapacity is corrected on the basis of the recognized degree ofdeterioration, a long time is needed to correct the capacity. Toactually measure the degree of deterioration of the battery pack by themethod as described above, the charging and discharging operation of thebattery pack needs to be performed once. Therefore, the degree ofdeterioration of the battery pack is actually measured so that thedeterioration of the battery pack is further accelerated.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a new battery packand a method for calculating the remaining capacity of a battery thatcan solve the above-described problems of a usual battery pack.

It is another object of the present invention to provide a battery packand a method for calculating the remaining capacity of a battery inwhich the decrease of capacity based on not only the number of times ofcharging and discharging operations, but also using conditions andstorage conditions or the like can be simply corrected and the remainingcapacity of the battery as a value extremely near to an actual remainingcapacity can be detected.

As the deterioration of a battery pack using a battery cell that can becharged is progresses, internal impedance is increased. Accordingly,when a new battery pack undergoes a constant voltage charging operation,since the internal impedance is low, much electric current is allowed toflow upon start of charging operation, a quantity of electric currentflowing during the charging operation is rapidly decreased and thebattery pack is completely charged for a short charging time (h₁). Onthe other hand, when a deteriorated battery pack undergoes a constantvoltage charging operation, since the internal impedance is high, asmall quantity of electric current flows upon start of chargingoperation and the quantity of electric current flowing during thecharging operation is slowly decreased to require a long charging time(h₂).

The inventors of the present invention eagerly continuously studied toachieve the above-described objects. Then, they recognized that since acharging current changed upon charging operation as shown in B in FIG. 1in the deteriorated battery pack, and the charging current changed uponcharging operation as shown in A in FIG. 1 in the new battery pack, anintegrated quantity of electric current flowing after the chargingcurrent reached a reference current value Ix was more in thedeteriorated battery pack than that in the new battery pack.

A battery pack mounted on an external device according to the presentinvention comprises: a battery cell that is charged and discharged; acurrent detecting means for detecting electric current flowing when thebattery cell is charged and discharged; a capacity integrated valuecalculating means for calculating a capacity integrated value byintegrating the electric current; a reset means for resetting thecapacity integrated value to a reference capacity integrated value whenthe current detected by the current detecting means reaches a prescribedvalue; a storing means for storing a maximum capacity integrated valueand the reference capacity integrated value; and a data calculatingmeans for calculating a remaining capacity data of a battery on thebasis of the capacity integrated value. The capacity integrated valuecalculating means integrates the current by regarding the referencecapacity integrated value as a reference. The data calculating meansdetermines the capacity integrated value calculated by the capacityintegrated value calculating means as the remaining capacity data of thebattery when the capacity integrated value calculated by the capacityintegrated value calculating means is smaller than the maximum capacityintegrated value and determines the maximum capacity integrated value asthe remaining capacity data of the battery when the capacity integratedvalue calculated by the capacity integrated value calculating means isnot smaller than the maximum capacity integrated value.

Another battery pack mounted on an external device according to thepresent invention comprises: a battery cell that is charged anddischarged; a current detecting means for detecting electric currentflowing when the battery cell is charged and discharged; a capacityintegrated value calculating means for calculating a capacity integratedvalue by integrating the electric current; a reset means for resettingthe capacity integrated value to a reference capacity integrated valuewhen the current detected by the current detecting means reaches aprescribed value; a storing means for storing a maximum capacityintegrated value and the reference capacity integrated value; reachingtime counting means for counting a number of times that the capacityintegrated value calculated by the capacity integrated value calculatingmeans reaches the maximum capacity integrated value; and a referencecapacity integrated value correcting means for correcting the referencecapacity integrated value on the basis of the number of times counted bya reaching time counting means. The capacity integrated valuecalculating means integrates the current on the basis of the referencecapacity integrated value to calculate the capacity integrated value anddetermines the capacity integrated value as the remaining capacity dataof a battery.

A method for calculating a remaining capacity of a battery of a batterypack mounted on an external device according to the present inventioncomprises: a current detecting step of detecting electric currentflowing when the battery cell provided in the battery pack is chargedand discharged; a capacity integrated value calculating step ofcalculating a capacity integrated value by integrating the electriccurrent; a resetting step of resetting the capacity integrated value toa reference capacity integrated value when the current reaches aprescribed value; and a data calculating step of calculating theremaining capacity data of a battery on the basis of the capacityintegrated value. In the capacity integrated value calculating step, thecurrent is integrated on the basis of the reference capacity integratedvalue. In the data calculating step, the capacity integrated valuecalculated in the capacity integrated value calculating step is comparedwith a maximum capacity integrated value stored in a storing means, andthe capacity integrated value calculated in the capacity integratedvalue calculating step is determined as the remaining capacity data ofthe battery when the capacity integrated value calculated in thecapacity integrated value calculating step is smaller than the maximumcapacity integrated value and the maximum capacity integrated value isdetermined as the remaining capacity data of the battery when thecapacity integrated value calculated in the capacity integrated valuecalculating step is larger than the maximum capacity integrated value.

Another method for calculating a remaining capacity of a battery of abattery pack mounted on an external device according to the presentinvention comprises: a current detecting step of detecting electriccurrent flowing when the battery cell provided in the battery pack ischarged and discharged; a capacity integrated value calculating step ofcalculating a capacity integrated value by integrating the electriccurrent; a resetting step of resetting the capacity integrated value toobtain a reference capacity integrated value when the current reaches aprescribed value; a reaching time counting step of counting the numberof times that the capacity integrated value calculated in the capacityintegrated value calculating step reaches a maximum capacity integratedvalue stored in a storing means; and a first reference capacityintegrated value correcting step of correcting the reference capacityintegrated value stored in the storing means on the basis of the numberof times counted in the reaching time counting step. In the capacityintegrated value calculating step, the current is integrated on thebasis of the reference capacity integrated value to calculate thecapacity integrated value and the capacity integrated value isdetermined as the remaining capacity data of the battery.

Still another objects of the present invention and specific advantagesobtained by the present invention will become more apparent from theexplanation of embodiments described below by referring to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the change of a capacity integrated valuewhen a battery pack is charged under a state that the deterioration ofthe battery pack progresses.

FIG. 2 is a block diagram showing a specific structure of a battery packaccording to the present invention.

FIG. 3 is a diagram showing the change of a capacity integrated value, amaximum capacity integrated value and a reference capacity integratedvalue when a new battery pack is charged.

FIG. 4 is a diagram showing the change of the capacity integrated valuewhen the battery pack is charged and a state that the capacityintegrated value is rest to the reference capacity integrated value whenthe value of electric current passing a seventh resistance is Ix.

FIG. 5 is a diagram showing the change of a quantity of electric currentpassing the seventh resistance when the battery pack undergoes aconstant voltage charging operation.

FIG. 6 is a diagram showing that a microcomputer outputs the maximumcapacity integrated value as the remaining capacity data of a batterywhen the capacity integrated value is not smaller than the maximumcapacity integrated value.

FIG. 7 is a diagram showing the change of the remaining capacity data ofthe battery when the reference capacity integrated value is corrected onthe basis of a number of times of reaches.

FIG. 8 is a flow chart showing the flow of processes when themicrocomputer counts the number of times of reaches.

FIG. 9 is a flow chart showing the flow of processes when themicrocomputer corrects the reference capacity integrated value.

FIG. 10 is a diagram showing the change of the remaining capacity dataof the battery when the microcomputer corrects the reference capacityintegrated value Y0 on the basis of a number of times of charging anddischarging operations in addition to the number of times of reaches.

FIG. 11 is a diagram sowing the change of the reference capacityintegrated value in accordance with a correction.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, a battery pack and a method for calculating a remaining capacity ofa battery according to the present invention will be described indetail.

A battery pack 1 according to the present invention comprises, as shownin FIG. 2, a battery cell 2 that is charged and discharged, a chargingand discharging current detecting circuit 3 for detecting electriccurrent for charging and discharging the battery cell 2, a communicationcircuit 4, a microcomputer 5, a power source 6 of a microcomputer, atemperature sensor 7, a voltage detecting circuit 8, a nonvolatilememory 9 and a two input NAND gate 10.

The battery pack 1 is connected to or incorporated in an electronicdevice such as a video camera, a portable telephone or a personalcomputer and used as a power source of the electronic device.

In the battery pack 1 according to the present invention, a cathode ofthe battery cell 2 is connected to a plus terminal TM+ of the batterypack 1 and an anode of the battery cell 2 is connected to a minusterminal TM− of the battery pack 1 through a below-described seventhresistance.

The charging and discharging current detecting circuit 3 detectselectric current flowing when the battery pack 1 is charged anddischarged to supply the electric current to the microcomputer 5. Thecharging and discharging current detecting circuit 3 includes a chargingcurrent detecting part 16 having a first resistance 11, a secondresistance 12, a third resistance 13, a first switching transistor 14and an operational amplifier 15 for charging current, a dischargingcurrent detecting part 26 having a fourth resistance 21, a fifthresistance 22, a sixth resistance 23, a second switching transistor 24and an operational amplifier 25 for discharging current and a seventhresistance 27. The detailed operation of the charging and dischargingcurrent detecting circuit 3 will be described below.

The communication circuit 4 includes a buffer amplifier 31 for inputtingdata and a buffer amplifier 32 for outputting data. The buffer amplifier31 for inputting the data is connected to a data input terminal 51provided in the microcomputer 5. The buffer amplifier 32 for outputtingthe data is connected to a data output terminal 52 provided in themicrocomputer 5. The communication circuit 4 outputs data Sout outputtedfrom the data output terminal 52 through the buffer amplifier 32 foroutputting the data. The data outputted from the communication circuit 4is supplied to an external device (not shown) such as the electronicdevice. Further, the communication circuit 4 supplies data Sin suppliedfrom the external device is supplied to the data input terminal 51through the buffer amplifier 31 for inputting the data.

The microcomputer 5 generates data showing the state of the battery pack1. The microcomputer 5 integrates the electric current detected by thecharging and discharging current detecting circuit 3 to calculate acapacity integrated value Y showing the remaining capacity of thebattery pack 1. The microcomputer 5 counts the number of times that thebattery pack 1 is charged and discharged. Further, the microcomputer 5performs a communication between the external device and themicrocomputer, for instance, the output of the remaining capacity dataof a battery to the external device. The detail of the microcomputer 5will be described later.

The microcomputer power source 6 serves as a power source of themicrocomputer 5. The microcomputer power source 6 includes a seriesregulator or a reset circuit or the like. The microcomputer power source6 is connected to a power terminal 53 provided in the microcomputer 5 tosupply power V to the microcomputer 5 through the power terminal 53.

The temperature sensor 7 is composed of, for instance, a temperaturedetecting thermistor. The temperature sensor 7 is disposed at a positionnear the battery cell 2 or coming into contact with the battery cell 2.A temperature detected value DT of the temperature sensor 7 is suppliedto a temperature detecting input terminal 54 of the microcomputer 5.Accordingly, the microcomputer 5 can recognize the temperature of thebattery cell 2 on the basis of the temperature detected value DTsupplied to the temperature detecting input terminal 54.

The voltage detecting circuit 8 detects voltage between terminals of thebattery cell 2 by a voltage dividing resistance composed of an eighthresistance 35 and a ninth resistance 36. A voltage detected value DVfrom the voltage detecting circuit 8 is supplied to a voltage detectinginput terminal 55 of the microcomputer 5. Accordingly, the microcomputer5 can recognize voltage between terminals of the battery cell 2 on thebasis of the voltage detected value DV supplied to the voltage detectinginput terminal 55.

The nonvolatile memory 9 stores a maximum capacity integrated value Ym,a reference capacity integrated value Y0 and a reference current valueIx. The nonvolatile memory 9 is connected to a cycle data input terminal56 provided in the microcomputer 5. The maximum capacity integratedvalue Ym, the reference capacity integrated value Y0 and the referencecurrent value Ix stored in the nonvolatile memory 9 are inputted to thecycle data input terminal 56. As the maximum capacity integrated valueYm, a value slightly larger than the capacity of the battery pack 1 as anew product is employed as shown in FIG. 3. In the present invention, asa capacity integrated value Ys obtained when the battery pack 1 as a newproduct that has not been yet charged upon shipment is charged by usingthe reference capacity integrated value Y0, a capacity integrated valueof 90% as high as a full charge is used. Further, in the battery pack 1according to the present invention, as the reference current value Ix, acurrent value I is used when the battery pack 1 of a new product thathas not been yet charged upon shipment is charged to obtain a capacityintegrated value Y equal to the reference capacity integrated value Y0.

In the two input NAND gate 10, one of two input terminals is connectedto the output terminal of the operational amplifier 15 for chargingcurrent. The other of the two input terminals is connected to the outputterminal of the operational amplifier 25 for discharging current. Thetwo input NAND gate 10 has an output terminal connected to the powerterminal 53 through a tenth resistance 37. The two input NAND gateswitches the operation mode of the microcomputer 5.

Now, the charging and discharging current detecting circuit 3 will bedescribed in detail.

A noninverting input terminal of the operational amplifier 15 forcharging current is connected to the anode of the battery cell 2 throughthe third resistance 13 and the seventh resistance 27. An invertinginput terminal is connected to the second resistance 12 as a negativefeedback resistance for setting an amplification factor and the firstresistance 11. Further, the operational amplifier 15 for chargingcurrent is connected to a charging current detecting input terminal 57.Accordingly, from the output terminal of the operational amplifier 15for charging current, a voltage value is outputted that is obtained byamplifying a value of electric current flowing in the battery pack 1upon charging operation in accordance with a ratio of a resistance valueof the first resistance 11 to a resistance value of the secondresistance 12. The outputted voltage value is supplied to the chargingcurrent detecting input terminal 57.

The noninverting input terminal of the operational amplifier 25 fordischarging current is connected to the anode of the battery cell 2through the sixth resistance 23 and the seventh resistance 27. Theinverting input terminal is connected to the fifth resistance 22 as anegative feedback resistance for setting an amplification factor and thefourth resistance 21. Further, the operational amplifier 25 fordischarging current is connected to a discharging current detectinginput terminal 58. Accordingly, from the output terminal of theoperational amplifier 25 for discharging current, a voltage value isoutputted that is obtained by amplifying a value of electric currentflowing in the battery pack 1 upon discharging operation in accordancewith a ratio of a resistance value of the fourth resistance 21 to aresistance value of the fifth resistance 22. The outputted voltage valueis supplied to the discharging current detecting input terminal 58.

The first switching transistor 14 is composed of, for instance, a fieldeffect transistor and has its gate connected to a switching controloutput terminal 59 of the microcomputer 5. Between the drain and thesource of the first switching transistor 14, the first resistance 11 isconnected. Accordingly, when a signal level from the switching controloutput terminal 59 of the microcomputer 5 becomes, for instance, a high(H) level, the first switching transistor 14 is turned ON. Thus, theresistance value by the first resistance 11 is composed only of theresistance of the first switching transistor 14 that is substantiallyzero and the amplification factor of the operational amplifier 15 forcharging current is increased. On the other hand, when the signal levelfrom the switching control output terminal 59 of the microcomputer 5becomes, for instance, a low (L) level, the first switching transistor14 is turned OFF and the amplification factor of the operationalamplifier 15 for charging current is an amplification factor meeting aratio of the resistance value of the first resistance 11 to theresistance value of the second resistance 12, that is, an amplificationfactor smaller than that when the first switching transistor 14 isturned ON.

The second switching transistor 24 is also composed of a field effecttransistor and has its gate connected to a switching control outputterminal 60 of the microcomputer 5. Between the drain and the source ofthe second switching transistor 24, the fourth resistance 21 isconnected. Accordingly, when a signal level from the switching controloutput terminal 60 of the microcomputer 5 becomes, for instance, a high(H) level, the second switching transistor 24 is turned ON. Thus, theresistance value by the fourth resistance 21 is composed only of theresistance of the second switching transistor 24 that is substantiallyzero and the amplification factor of the operational amplifier 25 isincreased. On the other hand, when a signal level from the switchingcontrol output terminal 60 of the microcomputer 5 becomes, for instance,a low (L) level, the second switching transistor 24 is turned OFF andthe amplification factor of the operational amplifier 25 for dischargingcurrent is an amplification factor meeting the ratio of the resistancevalue of the fourth resistance 21 to the resistance value of the fifthresistance 22, that is, an amplification factor smaller than that whenthe second switching transistor 24 is turned ON.

Here, during an ordinary operation mode (during running), themicrocomputer 5 always monitors the levels of the charging currentdetecting input terminal 57 and the discharging current detecting inputterminal 58. When the levels of the charging current detecting inputterminal 57 and the discharging current detecting input terminal 58 arenot lower than prescribed levels, the microcomputer 5 sets both thesignal levels of the switching control output terminals 59 and 60 to low(L) levels. Thus, both the first switching transistor 14 and the secondswitching transistor 24 are turned OFF so that the amplification factorsof the operational amplifier 15 for charging current and the operationalamplifier 25 for discharging current are decreased. Accordingly, themicrocomputer 5 in the ordinary operation mode (upon running), may useoutput values from the operational amplifier 15 for charging current andthe operational amplifier 25 for discharging current in which theamplification factors are low to measure a current value flowing in thebattery pack 1 upon charging or discharging. Consequently, the values ofelectric current flowing upon charging and discharging operations aremeasured so that charging and discharging current integrated values canbe calculated.

On the other hand, upon ordinary operation mode (upon running), when thecharging and discharging current flowing in the battery pack 1 becomes asmall current whose current value is a prescribed value or smaller,outputs from the operational amplifier 15 for charging current and theoperational amplifier 25 for discharging current in which theamplification factors are low are also decreased. That is, the levels ofthe charging current detecting input terminal 57 and the dischargingcurrent detecting input terminal 58 also become low. When the levels ofthe charging current detecting input terminal 57 and the dischargingcurrent detecting input terminal 58 are prescribed levels or lower andthis state continues for a prescribed time, the microcomputer 5 decidesthat this state is a non-load state to shift to a power saving mode(sleep mode). Consumed power upon power saving mode is lower than thatupon ordinary operation mode, so that the energy of a circuit can besaved.

The microcomputer 5 under the power saving mode sets the signal levelsof the switching control output terminals 59 and 60 to high (H) level.Thus, the first switching transistor 14 and the second switchingtransistor 24 are turned ON and the amplification values of theoperational amplifier 15 for charging current and the operationalamplifier 25 for discharging current are increased. Accordingly, themicrocomputer 5 under the power saving mode can measure the currentvalue of the small current flowing through the battery pack 1 uponcharging or discharging by using output values from the operationalamplifier 15 for charging current and the operational amplifier 25 fordischarging current in which the amplification factors are high.

Here, upon power saving mode, when the current value of the charging ordischarging current becomes a prescribed value or higher, both outputvalues from the operational amplifier 15 for charging current and theoperational amplifier 25 for discharging current in which theamplification factors are low are also increased. That is, the levels oftwo input terminals of the two input NAND gate 10 become high levels, sothat the output of the two input NAND gate 10 becomes a low level. Asdescribed above, when the level of the output of the two input NAND gate10 supplied to an interrupt input terminal becomes the low level, themicrocomputer 5 releases the power saving mode to shift to the ordinaryoperation mode.

As described above, since the battery pack 1 has the consumed power uponpower saving mode lower than that upon ordinary operation mode, theenergy of the circuit can be saved. Further, in the battery pack 1, themicrocomputer 5 controls the first switching transistor 14 to be turnedON/OFF by a switching control output SW1 inputted to the switchingcontrol output terminal 59 and controls the second switching transistor24 to be turned ON/OFF by a switching control output SW2 inputted to theswitching control output terminal 60. Accordingly, in the battery pack1, the amplification factors of the operational amplifier 15 forcharging current and the operational amplifier 25 for dischargingcurrent can be changed. Thus, the small current can be detected uponpower saving mode and the current value can be measured upon ordinaryoperation mode at the same time by the above-described structure.

Now, the microcomputer 5 will be described below in detail.

The charging current detecting input terminal 57 of the microcomputer 5is connected to the output terminal of the operational amplifier 15 forcharging current and the discharging current detecting input terminal 58is connected to the output terminal of the operational amplifier 25 fordischarging current. Further, the interrupt input terminal 63 of themicrocomputer 5 is connected to the output terminal of the two inputNAND gate 10 having two input terminals to which the output terminals ofthe operational amplifier 15 for charging current and the operationalamplifier 25 for discharging current are respectively connected.Further, the output terminal of the two input NAND gate 10 is connectedto the power terminal 53 through the tenth resistance 37. Further, thetemperature detecting input terminal 54 of the microcomputer 5 isconnected to the output terminal 72 of the temperature sensor 7. Thecycle data input terminal 56 is connected to the output terminal 73 ofthe nonvolatile memory 9 and a ground terminal 62 is connected to theanode of the battery cell 2.

The microcomputer 5 calculates the capacity integrated value Y on thebasis of the reference capacity integrated value Y0 stored in thenonvolatile memory 9 and calculates the remaining capacity data of abattery on the basis of the capacity integrated value Y. Further, themicrocomputer 5 outputs the calculated remaining capacity of the batteryto the external device. Further, the microcomputer 5 corrects thereference capacity integrated value Y0 on the basis of the number oftimes that the capacity integrated value Y reaches the maximum capacityintegrated value Ym and the number of times that the battery pack 1 ischarged and discharged.

The microcomputer 5 calculates the current value to calculate thecapacity integrated value Y. As shown in FIG. 4, the microcomputer 5resets the capacity integrated value Y to the reference capacityintegrated value Y0 every time the current value of charging current Ioafter a constant voltage charging operation becomes Ix to calculate thecapacity integrated value Y. Further, the microcomputer 5 determines thecapacity integrated value Y calculated when the capacity integratedvalue Y is smaller than the maximum capacity integrated value Ym, as theremaining capacity data of the battery. When the capacity integratedvalue Y is not smaller than the maximum capacity integrated value Ym,the microcomputer 5 determines the maximum capacity integrated value Ymas the remaining capacity data of the battery.

A principle that the capacity integrated value Y calculated in themicrocomputer 5 becomes the maximum capacity integrated value Ym orlarger is described below.

In the battery pack 1 according to the present invention, as thedeterioration of the battery pack progresses, the internal impedance ofthe battery cell 2 is increased. That is, when the new battery pack 1undergoes a constant voltage charging operation, the internal impedanceof the battery cell 2 is low. Thus, a large quantity of electric currentis supplied to the seventh resistance 27 upon start of the chargingoperation as shown in A of FIG. 5. The quantity of supplied electriccurrent is rapidly decreased and the charging operation is completed fora prescribed time (h₁). On the other hand, when the deteriorated batterypack 1 undergoes the constant voltage charging operation, since theinternal impedance of the battery cell 2 is high, a quantity of electriccurrent supplied to the seventh resistance 27 upon start of the chargingoperation is small. The decrease of the quantity of supplied electriccurrent is slow and it takes time (h₂) longer than the above prescribedtime (h₁) until the charging operation is completed as shown in B ofFIG. 5.

Therefore, when the deteriorated battery pack 1 is subjected to theconstant voltage charging operation, the battery pack 1 is not yetcharged to 90% as much as a full-charge when the current value reachesIx. Further, when the deteriorated battery pack 1 undergoes the constantvoltage charging operation, the quantity of electric current supplied tothe seventh resistance 27 after the current value reaches Ix is largerthan that of the new battery pack 1.

In accordance with the above-described reasons, when the microcomputer 5resets the capacity integrated value Y to the reference capacityintegrated value Y0 every time the current value reaches Ix after theconstant voltage charging operation is performed to calculate thecapacity integrated value Y, the capacity integrated value in thedeteriorated pack 1 changes upon charging operation as shown in D ofFIG. 1, and the capacity integrated value changes in the new batterypack 1 as shown in C of FIG. 1. That is, in the deteriorated batterypack 1, the capacity integrated value Y obtained when the battery packis fully charge is larger than that of the new battery pack 1. Themaximum capacity integrated value Ym is set to a value slightly largerthan the capacity integrated value Y when the new battery pack 1 isfully charged. Accordingly, as the deterioration of the battery pack 1progresses, the capacity integrated value Y upon full charge is higherthan the maximum integrated value Ym to reach the maximum capacityintegrated value Ym.

Accordingly, when the capacity integrated value Y is the maximumcapacity integrated value Ym or higher, the microcomputer 5 outputs themaximum capacity integrated value Ym to the external device as theremaining capacity data of the battery. Thus, the remaining capacitydata of the battery of the battery pack 1 is outputted as shown in E ofFIG. 6 to prevent the maximum capacity integrated value from beingextremely larger than the capacity of the new battery pack 1.Consequently, for instance, when the remaining capacity of the batterypack 1 is displayed in an electronic device, the displayed remainingcapacity of the battery pack 1 can be prevented from being extremelyhigher than the capacity obtained when the new battery pack 1 is fullycharged.

Further, the microcomputer 5 corrects the reference capacity integratedvalue Y0 on the basis of the number of times (refer it to as the numberof time of reaches, hereinafter) that the capacity integrated value Yreaches the maximum capacity integrated value Ym.

As described above, since the internal impedance of the battery cell 2is high in the deteriorated battery pack 1, the quantity of electriccurrent supplied to the seventh resistance 27 upon start of the chargingoperation is decreased to make the decrease of the quantity of suppliedelectric current slow. Accordingly, when the current value reaches Ix,the battery pack is not yet charged to 90% as much as a full charge.That is, in the battery pack 1, as the deterioration of the battery pack1 progresses, an actual capacity integrated value obtained when thecurrent value reaches Ix is smaller than the reference capacityintegrated value Y0.

Further, when the deterioration of the battery pack 1 progresses, thecapacity integrated value Y upon full charge is larger than the maximumcapacity integrated value Ym so that the number of times that thecapacity integrated value Y reaches the maximum capacity integratedvalue Ym is increased. That is, the number of times of reaches indicatesthe degree of deterioration of the battery pack 1.

Therefore, the reference capacity integrated value Y0 is corrected onthe basis of the number of times of reaches in such a way that everytime the number of times of reaches in the battery pack 1 increases, forinstance, 10 times, the value of the reference capacity integrated valueY0 is corrected to have 95% as high as a value before the correction.Thus, in the battery pack 1, the remaining capacity data of the batterycan be corrected on the basis of the actual capacity of the battery pack1. Accordingly, in the battery pack 1, the remaining capacity data ofthe battery can be corrected on the basis of the deterioration due tothe storage conditions or using conditions as well as the number oftimes of charging and discharging operations. In the battery pack 1, asshown in F of FIG. 7, the remaining capacity of the battery can becorrected so as to be near to the actual remaining capacity of thebattery of the battery pack 1.

Further, in the battery pack 1, both corrections mentioned below arecarried out. That is, the correction of the remaining capacity data ofthe battery is carried out that when the capacity integrated value Ybecomes the maximum capacity integrated value Ym or larger, the maximumcapacity integrated value Ym is stored for the external device as theremaining capacity data of the battery. The correction of the referencecapacity integrated value Y0 on the basis of the number of times ofreaches is carried out. Thus, the remaining capacity data outputted bythe microcomputer 5 is determined to be a more precisely correctedreference capacity correction value Yh and has a value nearer to theactual remaining capacity of the battery of the battery pack 1.

In the present invention, the reference capacity integrated value Y0corrected on the basis of the number of times of reaches is stored inthe nonvolatile memory 9.

A method for counting the number of times of reaches in themicrocomputer 5 is described below.

As shown in FIG. 8, in step ST1, whether or not charging current issupplied to the seventh resistance 27 is firstly detected. When thecharging current is supplied to the resistance, the procedure advancesto step ST2. When the charging current is not supplied to theresistance, the counting of the number of times of reaches is finished.

Then, in the step ST2, whether or not the capacity integrated value Y issmaller than the maximum integrated value Ym is detected. When thecapacity integrated value Y is smaller than the maximum capacityintegrated value Ym, the count of the number of times of reaches isfinished. When the capacity integrated value Y is not smaller than themaximum capacity integrated value Ym, the procedure advances to stepST3.

Then, in the step ST3, whether or not the capacity integrated value Yinitially reaches the maximum capacity integrated value Ym after adischarging operation is detected. When the capacity integrated value Yinitially reaches the maximum capacity integrated value Ym after thedischarging operation, the procedure advances to step ST4. When thecapacity integrated value Y does not initially reach the maximumcapacity integrated value Ym after the discharging operation, the countof the number of reaches is finished.

Then, in the step ST4, the number of a counter for counting the numberof times of reaches is increased by one.

Further, the microcomputer 5 corrects the reference capacity integratedvalue Y0 on the basis of the number of times of charging and dischargingoperations in the battery pack 1.

As causes of the deterioration of the battery pack 1, the number oftimes that the battery pack 1 is charged and discharged, the using andstorage conditions of the battery pack 1 or the like are exemplified.Accordingly, the reference capacity integrated value Y0 is corrected onthe basis of the number of times of charging and discharging operationsin the battery pack 1 in such a way that every time the number of timesof charging and discharging operations in the battery pack 1 increases,for instance, by 50 times, the value of the reference capacityintegrated value Y0 is corrected to have 95% as high as a value beforethe correction. Thus, the remaining capacity of the battery pack 1 canbe corrected so as to be nearer to the actual remaining capacity of thebattery of the battery pack 1. As a method for counting the number oftimes that the battery pack 1 is charged and discharged, a methoddisclosed in, for example, Japanese Patent Application Laid-Open No. hei9-243718 is exemplified.

In the battery pack 1, a method for correcting the reference capacityintegrated value Y0 is described below.

As shown in FIG. 9, in step ST11, whether or not the value of electriccurrent supplied to the seventh resistance 27 is Ix is firstly decided.When the value of the electric current supplied to the seventhresistance 27 is Ix, the procedure advances to step ST12. When the valueof the electric current supplied to the seventh resistance 27 is not Ix,the correction of the reference capacity integrated value Y0 isfinished.

Then, in the step ST12, whether or not the number of times of reaches isa number of times for correcting the reference capacity integrated valueY0 is decided. When the number of times of reaches is the number oftimes for correcting the reference capacity integrated value Y0, theprocedure advances to step ST13. When the number of times of reaches isnot the number of times for correcting the reference capacity integratedvalue Y0, the procedure advances to step ST14.

In the step ST13, after the reference capacity integrated value Y0 iscorrected on the basis of the number of times of reaches, the procedureadvances to the step ST14.

Then, in the step ST14, whether or not the number of times of chargingand discharging operations is a number of times for correcting thereference capacity integrated value Y0 is decided. When the number oftimes of charging and discharging operations is the number of times forcorrecting the reference capacity integrated value Y0, the procedure ismoved to step ST15. When the number of times of charging and dischargingoperation is not the number of times for correcting the referencecapacity integrated value Y0, the correction of the reference capacityintegrated value Y0 is finished.

Then, in the step ST15, after the reference capacity integrated value Y0is corrected on the basis of the number of times of charging anddischarging operations, the correction of the reference capacityintegrated value Y0 is finished.

Although the above embodiment is described as the structure that onlythe reference capacity integrated value Y0 is corrected, the maximumcapacity integrated value Ym may be corrected in addition thereto. Inthis case, assuming that the value of the maximum capacity integratedvalue Ym is, for instance, a value that about 15% as high as thereference capacity integrated value Y0 is added to a value of thereference capacity integrated value Y0, the maximum capacity integratedvalue Ym may be corrected in accordance with the correction of thereference capacity integrated value Y0.

As described above, in the battery pack 1, the microcomputer 5 correctsthe reference capacity integrated value Y0 on the basis of the number ofcharging and discharging operations as well as the number of times ofreaches to obtain the reference capacity integrated value Yh after thecorrection. Accordingly, in the battery pack 1, the remaining capacitydata of the battery calculated by the microcomputer 5 is more preciselycorrected as shown in G of FIG. 10 so that the remaining capacity can bedrawn nearer to the actual remaining capacity of the battery of thebattery pack 1.

Further, in the battery pack 1, the microcomputer 5 corrects thereference capacity integrated value Y0. That is, in the battery pack 1,software is changed so that the remaining capacity data of the batterycan be corrected, and the remaining capacity data of the battery can becorrected without increasing a cost.

As shown in FIG. 11, a lower limit is preferably provided to correct thereference capacity integrated value Y0. The lower limit is provided forcorrecting the reference capacity integrated value Y0. Thus, theexcessive correction of the capacity integrated value Y can beprevented.

As described above, in the battery pack 1, the maximum capacityintegrated value Ym is stored in the nonvolatile memory 9. When thecalculated capacity integrated value Y is smaller than the maximumcapacity integrated value Ym, the microcomputer 5 determines thecalculated capacity integrated value Y as the remaining capacity data ofthe battery. When the calculated capacity integrated value Y is notsmaller than the maximum capacity integrated value Ym, the microcomputer5 determines the maximum capacity integrated value Ym as the remainingcapacity data of the battery. Accordingly, in the battery pack 1, theremaining capacity data of the battery outputted by the microcomputer 5can be prevented from being extremely larger than the capacity of thenew battery pack 1.

Further, in the battery pack 1, the microcomputer 5 corrects thereference capacity integrated value Y0 on the basis of the number oftimes of reaches. Specifically, in the battery pack 1, the remainingcapacity data of the battery can be corrected in accordance with thedegree of deterioration of the battery pack 1. Therefore, in the batterypack 1, the remaining capacity data of the battery can be corrected inaccordance with the deterioration due to not only the number of times ofcharging and discharging operations, but also the storage conditions orthe using conditions. The remaining capacity data of the batterycalculated by the microcomputer 5 can be more precisely corrected sothat the remaining capacity of the battery can be drawn nearer to theactual remaining capacity of the battery of the battery pack 1.

The present invention is not limited to the above-described embodimentsexplained by referring to the drawing. It is apparent for a person withordinary skill in the art that various changes, substitutions orequivalence thereto may be made without departing a scope of attachedclaims and the gist thereof.

INDUSTRIAL APPLICABILITY

As described above, in the battery pack according to the presentinvention, the data calculating means determines the capacity integratedvalue calculated by the capacity integrated value calculating means asthe remaining capacity data of the battery when the capacity integratedvalue calculated by the capacity integrated value calculating means issmaller than the maximum capacity integrated value and determines themaximum capacity integrated value as the remaining capacity data of thebattery when the capacity integrated value calculated by the capacityintegrated value calculating means is not smaller than the maximumcapacity integrated value. Accordingly, in the battery pack according tothe present invention, the remaining capacity data of the battery can beprevented from being extremely larger than the capacity of the newbattery pack.

In the battery pack according to the present invention, the referencecapacity integrated value correcting means corrects the referencecapacity integrated value on the basis of the number of times that thecapacity integrated value reaches the maximum capacity integrated value.Consequently, in the battery pack according to the present invention,the remaining capacity data of the battery can be corrected inaccordance with the degree of deterioration. That is, in the batterypack according to the present invention, the remaining capacity data ofthe battery can be corrected on the basis of the deterioration due tonot only the number of times of charging and discharging operations, butalso the storage conditions or the using conditions. Thus, the remainingcapacity data of the battery can be drawn to a value near the actualremaining capacity of the battery.

Further, in the method for calculating the remaining capacity of thebattery according to the present invention, the capacity integratedvalue calculated in the capacity integrated value calculating step isdetermined as the remaining capacity data of the battery when thecapacity integrated value calculated in the capacity integrated valuecalculating step is smaller than the maximum capacity integrated valueand the maximum capacity integrated value is determined as the remainingcapacity data of the battery when the capacity integrated valuecalculated in the capacity integrated value calculating step is largerthan the maximum capacity integrated value. Consequently, according tothe method for calculating the remaining capacity of the battery of thepresent invention, the outputted remaining capacity data of the batterycan be prevented from being extremely larger than the capacity of thenew battery pack.

Still further, in the method for calculating the remaining capacity ofthe battery according to the present invention, the reference capacityintegrated value stored in the storing means is corrected on the basisof the number of times counted in the reaching time counting step in thefirst reference capacity integrated value correcting step. Accordingly,in the method for calculating the remaining capacity of the battery packaccording to the present invention, the remaining capacity data of thebattery can be corrected on the basis of the deterioration due to notonly the number of times of charging and discharging operations, butalso the storage conditions or the using conditions. Thus, the remainingcapacity data of the battery can be drawn to a value near the actualremaining capacity of the battery.

1. A battery pack mounted on an external device, the battery packcomprising: a battery cell that is charged and discharged; a currentdetecting means for detecting electric current flowing when the batterycell is charged and discharged; a capacity integrated value calculatingmeans for calculating a capacity integrated value by integrating theelectric current; a reset means for resetting the capacity integratedvalue to a reference capacity integrated value when the current detectedby the current detecting means reaches a prescribed value; a storingmeans for storing a maximum capacity integrated value and the referencecapacity integrated value; and a data calculating means for calculatinga remaining capacity data of a battery on the basis of the capacityintegrated value, wherein the capacity integrated value calculatingmeans integrates the current by regarding the reference capacityintegrated value as a reference, and the data calculating meansdetermines the capacity integrated value calculated by the capacityintegrated value calculating means as the remaining capacity data of thebattery when the capacity integrated value calculated by the capacityintegrated value calculating means is smaller than the maximum capacityintegrated value and determines the maximum capacity integrated value asthe remaining capacity data of the battery when the capacity integratedvalue calculated by the capacity integrated value calculating means isnot smaller than the maximum capacity integrated value.
 2. The batterypack according to claim 1, further comprising: a reaching time countingmeans for counting a number of times that the capacity integrated valuecalculated by the capacity integrated value calculating means reachesthe maximum capacity integrated value; and a reference capacityintegrated value correcting means for correcting the reference capacityintegrated value on the basis of the number of times counted by thereaching time counting means.
 3. The battery pack according to claim 2,wherein the reference capacity integrated value corrected by thereference capacity integrated value correcting means is a prescribedvalue or larger.
 4. The battery pack according to claim 1, furtherincluding a data output means for outputting the remaining capacity dataof the battery to the external device.
 5. The battery pack according toclaim 1, further including a charging and discharging time countingmeans for counting the number of times that the battery cell is chargedand discharged, wherein the reference capacity integrated valuecorrecting means corrects the reference capacity integrated value on thebasis of the number of times counted by the charging and dischargingtime counting means.
 6. A battery pack mounted on an external device,the battery pack comprising: a battery cell that is charged anddischarged; a current detecting means for detecting electric currentflowing when the battery cell is charged and discharged; a capacityintegrated value calculating means for calculating a capacity integratedvalue by integrating the electric current; a reset means for resettingthe capacity integrated value to a reference capacity integrated valuewhen the current detected by the current detecting means reaches aprescribed value; a storing means for storing a maximum capacityintegrated value and the reference capacity integrated value; a reachingtime counting means for counting a number of times that the capacityintegrated value reaches the maximum capacity integrated value; and areference capacity integrated value correcting means for correcting thereference capacity integrated value on the basis of the number of timescounted by the reaching time counting means, wherein the capacityintegrated value calculating means integrates the current on the basisof the reference capacity integrated value to calculate the capacityintegrated value and determines the capacity integrated value as theremaining capacity data of a battery.
 7. The battery pack according toclaim 6, wherein the reference capacity integrated value corrected bythe reference capacity integrated value correcting means is a prescribedvalue or larger.
 8. The battery pack according to claim 6, furtherincluding a data output means for outputting the remaining capacity dataof the battery to the external device.
 9. The battery pack according toclaim 6, further including a charging and discharging time countingmeans for counting a number of times that the battery cell is chargedand discharged, wherein the reference capacity integrated valuecorrecting means corrects the reference capacity integrated value on thebasis of the number of times counted by the charging and dischargingtime counting means.
 10. A method for calculating the remaining capacityof a battery of a battery pack mounted on an external device, the methodcomprising: a current detecting step of detecting electric currentflowing when a battery cell provided in the battery pack is charged anddischarged; a capacity integrated value calculating step of calculatinga capacity integrated value by integrating the electric current; aresetting step of resetting the capacity integrated value to a referencecapacity integrated value when the current reaches a prescribed value;and a data calculating step of calculating the remaining capacity dataof a battery on the basis of the capacity integrated value, wherein inthe capacity integrated value calculating step, the current isintegrated on the basis of the reference capacity integrated value, andin the data calculating step, the capacity integrated value calculatedin the capacity integrated value calculating step is compared with amaximum capacity integrated value stored in a storing means and thecapacity integrated value calculated in the capacity integrated valuecalculating step is determined as the remaining capacity data of thebattery when the capacity integrated value calculated in the capacityintegrated value calculating step is smaller than the maximum capacityintegrated value and the maximum capacity integrated value is determinedas the remaining capacity data of the battery when the capacityintegrated value calculated in the capacity integrated value calculatingstep is larger than the maximum capacity integrated value.
 11. Themethod for calculating the remaining capacity of a battery according toclaim 10, further comprising: a reaching time counting step of countinga number of times that the capacity integrated value calculated in thecapacity integrated value calculating step reaches the maximum capacityintegrated value; and a first reference capacity integrated valuecorrecting step of correcting the reference capacity integrated value onthe basis of the number of times counted in the reaching time countingstep.
 12. The method for calculating the remaining capacity of a batteryaccording to claim 11, wherein the reference capacity integrated valuecorrected in the first reference capacity integrated value correctingstep is a prescribed value or larger.
 13. The method for calculating theremaining capacity of a battery according to claim 10, further includinga data output step of outputting the remaining capacity data of thebattery to the external device.
 14. The method for calculating theremaining capacity of a battery according to claim 10, furthercomprising: a charging and discharging time counting step of counting anumber of times that the battery cell is charged and discharged, and asecond reference capacity integrated value correcting step of correctingthe reference capacity integrated value on the basis of the number oftimes counted by the charging and discharging time counting step. 15.The method for calculating the remaining capacity of a battery accordingto claim 14, wherein the reference capacity integrated value correctedin the second reference capacity integrated value correcting step is aprescribed value or larger.
 16. A method for calculating a remainingcapacity of a battery of a battery pack mounted on an external device,the method comprising: a current detecting step of detecting electriccurrent flowing when a battery cell provided in the battery pack ischarged and discharged; a capacity integrated value calculating step ofcalculating a capacity integrated value by integrating the electriccurrent; a resetting step of resetting the capacity integrated value toobtain a reference capacity integrated value when the current reaches aprescribed value; a reaching time counting step of counting the numberof times that the capacity integrated value calculated in the capacityintegrated value calculating step reaches a maximum capacity integratedvalue stored in a storing means; and a first reference capacityintegrated value correcting step of correcting the reference capacityintegrated value stored in the storing means on the basis of the numberof times counted in the reaching time counting step, wherein in thecapacity integrated value calculating step, the current is integrated onthe basis of the reference capacity integrated value to calculate thecapacity integrated value and the capacity integrated value isdetermined as the remaining capacity data of the battery.
 17. The methodfor calculating the remaining capacity of a battery according to claim16, wherein the reference capacity integrated value corrected in thefirst reference capacity integrated value correcting step is aprescribed value or larger.
 18. The method for calculating the remainingcapacity of a battery according to claim 16, further including a dataoutput step of outputting the remaining capacity data of the battery tothe external device.
 19. The method for calculating the remainingcapacity of a battery according to claim 16, further comprising: acharging and discharging time counting step of counting the number oftimes that the battery cell is charged and discharged, and a secondreference capacity integrated value correcting step of correcting thereference capacity integrated value stored in the storing means on thebasis of the number of times counted in the charging and dischargingtime counting step.
 20. The method for calculating the remainingcapacity of a battery according to claim 19, wherein the referencecapacity integrated value corrected in the second reference capacityintegrated value correcting step is a prescribed value or larger.